In my opinion validity In general, it is a rather vague term. On the other hand, the node uses the reference list to check the transaction. When all the standards are met, transactions are considered valid. One of those criteria is as follows:There must be a reference output for each input and cannot already be consumed.”(Antonopoulos, Bitcoin Masterp. 235). Therefore, if all inputs of the new transaction are utxos, the standard is confirmed.
At the same time, Antonopoulos points out when discussing “51% attack”:The more confirmation, the more difficult it is to invalidate the transaction with a 51%attack.This means that the transaction can be invalidated through the chain reorganization.
Therefore, from the point of view of miners, the effectiveness of the transaction is binary attributes. But from the point of view of a wider network, it’s probability.